QUITO, Ecuador  A volcano on the largest of the Galapagos Islands erupted for the third straight day Tuesday, but experts said it didn't threaten villagers on the island or the super-sized tortoises that gave the remote archipelago its name.

Oscar Carvajal, chief technician of the Galapagos National Park on Isabela island, said tortoises and land iguanas were not threatened because the lava flows were down the northeast slopes of Sierra Negra volcano where there were no animal populations.

"The lava flows have not affected the species because they are on the other side. There are no problems with tortoises or land iguanas. Only a small amount of vegetation has been burned in the interior of the caldron and on the flanks," Carvajal said.

The 4,920-foot high Sierra Negra volcano began erupting late Saturday, sending three rivers of spectacular lava flow down its northeastern slopes.

Carvajal said the lava expelled Tuesday was considerably less. He said most of the lava was flowing from a fissure at the top of the volcano back into the interior.

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Park and local authorities say Puerto Villamil, the island's only village with 2,000 inhabitants, is also out of danger because it is located south of the volcano.

Puerto Villamil mayor Pablo Gordillo said authorities have taken precautions and were ready to evacuate people by sea and air if necessary.

Patricio Roman, a technician at Ecuador's Geophysics Institute, said the eruption of Sierra Negra was a normal process for islands that are of volcanic origin. He said the archipelago, made up of 13 islands, only four of which have human inhabitants, is still young enough in geological terms to be in a process of formation.

"Sierra Negra volcano is very active, one of the most active volcanos in the Galapagos, and the Galapagos are considered one of the most active volcano centers in the world," he said.

"The Galapagos Islands are what geologists know as a hot point, a point that draws magma from the depths," he said.

Sierra Negra last erupted in 1979, but in May of this year La Cumbre volcano on nearby Fernandina island, which is uninhabited, erupted with water vapor, gas and ash. Another volcano on Isabela, Cerro Azul, erupted in 1998.

The Galapagos Islands, located 625 miles off Ecuador's Pacific coast, were declared a UNESCO World Heritage Site in 1979.

They are known for their flora and fauna, including marine iguanas, blue-footed boobies and giant tortoises that live up to 150 years of age. The islands' unique wildlife inspired Charles Darwin's theory of evolution.